Generally, the bandwidth of one wireless communication line is approximately several hundreds Mbps. In contrast, in the case of a user side communication line, it has a large bandwidth of, for example, 1 Gbps (bits per second) or 10 Gbps. In order to eliminate this bandwidth gap, it has been well known to employ the method of increasing the total bandwidth of the wireless communication line side by using a plurality of wireless communication lines. In this case, load balance control (also referred to as load sharing control) for balancing loads given to the respective wireless communication lines has been performed.
As an example of this load balance control, for example, load balance control by means of a so-called “round robin” method, in which loads (for example, transmitting packets or transmitting frames) are sequentially allocated to the individual wireless communication lines, can be taken. For example, in the case where a series of frames (1, 2, 3, 4, 5 . . . ) are sorted to two wireless communication lines, the frames 1, 3, 5 . . . are sorted to one line buffer, and the frames 2, 4 . . . are sorted to the other line buffer.
Further, in Patent Literature 1, there is described a load sharing technology, in which, for each of communication lines, an available remaining line capacity thereof is calculated on the basis of the difference between a preset threshold value and a current data-transmission amount thereof, and increased transmitting data or transmitting data having overflowed from a certain one of the communication lines is sorted to any communication lines thereof each having the available remaining line capacity.
Further, in Patent Literature 2, there is described another load sharing technology, in which, when the storage amount of data stored in a certain buffer (one of buffers provided for respective communication lines) has exceeded a preset storage-capacity threshold value thereof, the buffer is switched to another buffer, into which data having been received from an external network is stored.